Basic Research On Preparation Of Tantalum Powder By Multistage Depth Reduction Process

As a high melting point metal,niobium is widely used in electronics,chemical,machinery,alloys and weapon systems,it has also potential applications in medical fields such as artificial bones.At present,the preparation method of ruthenium is still based on the sodium reduction potassium fluoroantimonate method,and there are some defects like high preparation cost,high energy consumption,harsh operating conditions,and large pollution of this method.Aiming at the problems existing in the preparation method of the metal tantalum powder,a new idea of directly preparing metal tantalum powder by multi-stage deep reduction was proposed based on the systematically analyze of the thermodynamic transformation law and phase transformation law of the niobium oxide reduction process.This method firstly performs selfpropagation rapid reduction to obtain a non-stoichiometric low-valent cerium oxide intermediate,primary reduction;then the primary reduction intermediate is subjected to multistage deep reduction using a more reducing reducing agent to obtain a deep reduction product.Finally,the deep reduction product is subjected to enhanced acid leaching to obtain a metal cerium powder.This research focused on the basic scientific issues in primary reduction,deep reduction,and enhanced acid leaching and the main contents and conclusions of this paper are as follows:Firstly,the thermodynamics of the reduction of Ta₂O₅ by different reducing agents were studied.The results show that the adiabatic temperatures of the reaction system for the reduction of Ta₂O₅ by Mg and Ca to prepare metal niobium are 3098K and 2888K,respectively.When the thermodynamic criterion is more than 1800K,the reaction will occur in self-propagating form,and when it is lower than 900K,the ability of Ca(g),Mg(g),Ca,and Mg to reduce Ta₂O₅ is sequentially weakened.And with the increase of temperature,the ability of Ca(g),Ca,Mg(g)and Mg to reduce Ta₂O₅ is weakened,in turn until Mg-Ca gasification.And the reduction action of TaO will be promoted at a high partial pressure and a low temperature when calcium and magnesium are in the form of vapor,Secondly,the influence of process conditions on the primary reduction of Ta₂O₅ was investigated.The results showed that the primary reduction products are mainly MgO,Ta and by-product Mg₄Ta₂O₉ phase when the Ta₂O₅ were reduced by magnesium.The increase of magnesium content will promote the complete reduction of Ta₂O₅ to form coral-like Ta particles but the Mg₄Ta₂O₉ by-product phase still exists.The addition of MgO as a diluent will lower the adiabatic temperature of the reaction,and a gas-solid reaction occurred when the adiabatic temperature is lower than the melting point of Ta₂O₅.The primary reduction will be promoted by using the compact and the yield of the reaction product is remarkably improved.The reaction law is similar to that of the magnesium reduction process when the primary reduction is carried out using calcium as a reducing agent.Then,in order to investigate the removal rule of the magnesium ditantalum hexaoxide byproduct phase during leaching and purification,the formation of magnesium ditantalum hexaoxide during primary reduction was investigated by simulation.The results show that the Mg(Ta)composite oxides include MgTa₂O₆ and Mg₄Ta₂O₉.The MgTa₂O₆ starts to form when the synthesis temperature is 1000?,and Mg₄Ta₂O₉ starts to form at 1100?.When the synthesis temperature is lower than 1500 ?,MgTa₂O₆ is preferentially formed and the Mg₄Ta₂O₉ is preferentially formed when temperature is higher than 1500 ?.The MgTa₂O₆ will react with MgO to form Mg₄Ta₂O₉.When the molar ratio of Ta₂O₅ and MgO is lower thanl:4,the formation of Mg₄Ta₂O₉ will be hindered and promoted when the molar ratio of Ta₂O₅ and MgO is higher than 1:4.The dissolution behavior of magnesium ditantalum hexaoxide in hydrochloric acid showed that Mg₄Ta₂O₉ and MgTa₂O₆ did not react with hydrochloric acid,and the acid leaching could not remove the magnesium ditantalum hexaoxide by-product phase in the reaction product.Therefore,in order to prepare a highly pure metal ruthenium,it is necessary to control the formation of a magnesium ruthenate by-product phase in the reduction product and reduce it in depth.Finally,the effects of deep reduction process conditions on the deep removal of oxygen in the primary reduction products and the removal of impurity phases were investigated.The results showed that when choose the calcium as a reducing agent for deep reduction can effectively remove oxygen in the form of Ta-O solid solution or low-valent oxide,magnesium tantalate from the primary reduction product and remove the magnesium ditantalum hexaoxide at the same time.The deep reduction reaction process is a rapid reaction process,and the reaction equilibrium state can be achieved after 30 minutes,continuing to extend the reduction heat preservation time will cause the ruthenium particles to grow.When the deep reduction temperature is higher than 1100?,the content of calcium residue in the deep reduction product increases,and the optimum reduction temperature is 1000?.With the increase of the reducing agent dosage,the deep reduction product becomes fluffy and the total impurity content decreases.High purity tantalum powder with oxygen content lower than 0.0001%,impurities(calcium,magnesium,oxygen)total residual less than 0.05%was successfully prepared.